(a) Technical Field
The present invention relates to a non-PGM (platinum-group metals) catalyst for burning carbon soot having an improved oxidizing power at a low temperature, and a filtration filter and an exhaust gas post-processing apparatus using the same.
(b) Background Art
In recent years, an amount of exhaust gases exhausted from internal combustion engines are rapidly increasing due to a rapid increase in the number of vehicles. In particular, various substances contained in exhaust gases of diesel engines significantly influence the environment, and it is reported that soot in the exhaust gases can cause health issues, such as allergic disorders or decreased sperm count.
Thus, it is becoming an urgent research project to remove soot in exhaust gases. A commercialized soot removing apparatus includes a casing installed at an intermediate portion of an exhaust pipe connected to an exhaust manifold of an engine, and a filter (hereinafter, referred to as a “filtration filter”) having fine cells mounted within the casing.
Then, carbon soot in exhaust gas discharged through an exhaust pipe during an operation of a vehicle is deposited on cell walls of a filtration filter, so it is necessary to regularly remove the carbon soot.
As well known in the art, excellent technologies for removing captured soot using a catalyst include a passive regeneration method using the oxidizing power of NO2, and an active regeneration method of removing unburned hydrocarbons produced in an engine by generating oxidation heat in an oxidation catalyst and a filtration filter containing the oxidation catalyst.
In a method of removing captured soot, a high-priced platinum-based oxidation catalyst (platinum-group metal or PGM) is coated on a filtration filter to lower combustion temperature and improve fuel efficiency.
FIG. 1 is a schematic view for explaining a method of burning carbon soot by a DPF (Diesel Particulate Filter) catalyst using a PGM catalyst. As illustrated in FIG. 1, carbon soot filtrated by the DPF is burned when NO2 contained in exhaust gas discharged from an engine and NO2 oxidized by a catalyst, in which platinum (Pt) is coated on an alumina/mixture oxide, react with the platinum (Pt).
However, although a combustion temperature can be decreased by using a high-priced PGM such as platinum, the price of the catalyst is high, increasing the manufacturing costs of a vehicle.
Meanwhile, Japanese Patent No. 4144898 discloses a soot burning catalyst including a carrier consisting of a cerium-zirconium complex oxide containing 5 to 50 wt % of cerium oxide, and a first catalyst consisting of at least one of silver (Ag) and rubidium (Ru) impregnated in the carrier or its oxide and having 0.5 to 30 wt % of the carrier.
According to the Japanese patent, soot can be removed at a low temperature using an oxidation reaction without using a high-priced PGM.
Although the above Japanese patent discloses an advanced technology, considering that it does not use a PGM, there is still a need to improve a combustion efficiency of soot.